U.S. patent application number 12/144180 was filed with the patent office on 2008-10-23 for bidirectional optical amplifier.
Invention is credited to Luc Boivin, Dmitriy KRYLOV.
Application Number | 20080259438 12/144180 |
Document ID | / |
Family ID | 36205915 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080259438 |
Kind Code |
A1 |
KRYLOV; Dmitriy ; et
al. |
October 23, 2008 |
BIDIRECTIONAL OPTICAL AMPLIFIER
Abstract
A bidirectional amplification system and method are disclosed. A
single optical line amplifier and isolation loss filters are used
to amplify signals in both the east and west directions with
sufficient gain along a fiber.
Inventors: |
KRYLOV; Dmitriy; (Red Bank,
NJ) ; Boivin; Luc; (Tinton Falls, NJ) |
Correspondence
Address: |
Muncy, Geissler, Olds & Lowe, PLLC
P.O. BOX 1364
FAIRFAX
VA
22038-1364
US
|
Family ID: |
36205915 |
Appl. No.: |
12/144180 |
Filed: |
June 23, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11041927 |
Jan 26, 2005 |
7408702 |
|
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12144180 |
|
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60621516 |
Oct 25, 2004 |
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Current U.S.
Class: |
359/349 |
Current CPC
Class: |
H01S 3/06787 20130101;
H01S 3/06754 20130101 |
Class at
Publication: |
359/349 |
International
Class: |
H01S 3/00 20060101
H01S003/00 |
Claims
1. An optical amplifier module, comprising: a first band-splitting
module (BSM) coupled to a first communication fiber to receive a
first signal propagating in a first direction; a second BSM coupled
to a second communication fiber to receive a second signal
propagating in a second direction; an amplifier; a third BSM
coupled to the first BSM receive the first signal, coupled to the
second BSM to receive the second signal, and coupled to the
amplifier, wherein the third BSM is configured to combine the first
and the second signals and provide the combined signals traveling
in a common direction to the amplifier; a fourth BSM coupled to the
amplifier and configured to separate the combined signals into
amplified first and amplified second signals; a first filter
coupled between the first BSM and the fourth BSM to receive the
amplified second signal from the fourth BSM and to propagate the
amplified second signal to the first BSM, wherein the first BSM is
configured to direct the amplified second signal to the first
communication fiber; and a second filter configured to receive the
amplified first signal from the fourth BSM and to propagate the
amplified first signal to the second BSM, wherein the second BSM is
configured to direct the amplified first signal to the second
communication fiber.
2. The amplifier module of claim 1, wherein the first filter is
configured to increase an isolation loss.
3. The amplifier module of claim 2, wherein the first filter
increases the isolation loss by approximately 20 dB.
4. The amplifier module of claim 1, wherein the second filter is
configured to increase an isolation loss.
5. The amplifier module of claim 4, wherein the second filter
increases the isolation loss by approximately 20 dB.
6. The amplifier module of claim 1, wherein at least one of the
first and second filters is a band splitting module.
7. The amplifier module of claim 6, wherein two ports of the band
splitting module are used to form the at least one of the first and
second filters.
8. The amplifier module of claim 1, wherein isolation loss
characteristics are substantially similar for the first, second,
third and fourth band splitting modules.
9. The amplifier module of claim 1, wherein the first and second
filters are each a band splitting module and wherein isolation loss
characteristics are substantially similar for all band splitting
modules.
10. The amplifier module of claim 1, wherein at least one of the
first filter and second filter is at least one of a thin-film
filter, a fiber Bragg grating (FBG) filter, and an array waveguide
(AWG) filter.
11. The amplifier module of claim 1, wherein the first signal
comprises a first plurality of wavelengths in a first band and the
second signal comprises a second plurality of wavelengths in a
second band.
12. The amplifier module of claim 11, wherein the amplified first
signal comprises the first plurality of wavelengths in the first
band and wherein the amplified second signal comprises the second
plurality of wavelengths in the second band.
13. The amplifier module of claim 12, wherein at least one of the
first signal and the second signal is at least one of a dense wave
division multiplexed (DWDM) signal and a wave division multiplexed
(WDM) signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/041,927, which was filed on Jan. 26, 2005 and which claims
priority to U.S. Provisional Patent Application No. 60/621,516
filed on Oct. 25, 2004 and which are both herein incorporated by
reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to signal amplifiers, in
particular to optical bidirectional signal amplifier nodes.
BACKGROUND OF THE INVENTION
[0003] In current large-scale networks, information flows through a
series of nodes in the network from one location or site to
another. As the network grows, more and more transmission lines may
be added to handle the heavy traffic flow between nodes. FIG. 1
illustrates a related art system 100 that has east 110 and west 140
terminals. The east 110 and west 140 terminals communicate via
lines (e.g., lines 152, 154, 156 and 162, 164, 166) that run
between the terminals (e.g., optical fiber pairs 156 and 166, 164
and 154, 152 and 162. East 110 and west 140 terminals can be
located a significant distance apart.
[0004] Accordingly, line amplifier nodes (e.g., 120, 130) can be
interposed between the terminals (e.g., every 40-80 kilometers) to
compensate for the signal loss in the transmission medium (e.g.,
optical fiber) by amplifying the signal. Additionally, associated
dispersion compensation modules (e.g., DCMs 122, 128, 132 and 138)
can be added to correct for the signal degradation caused by the
transmission medium (e.g., dispersion in the optical fibers).
Further, to increase the bandwidth available each east and west
line can have a plurality of channels communicated on separate
bands (e.g., red and blue signals), as is known in the art.
[0005] If the bandwidth provided by both bands is not needed for
each direction, a single fiber can be used to carry both directions
using one band for the east direction and one band for the west.
There are several implementations of a bidirectional optical
communication on a single fiber. These single-fiber implementations
use counter-propagating channels from two non-overlapping bands of
the optical spectrum. Although this system configuration can reduce
the number of fibers for bidirectional communication, it can
further complicate design of the amplifier nodes. For example, in
one solution the red and blue signals are separated at respective
inputs, routed through separate amplifiers, and then recombined at
the respective outputs. However, this configuration still requires
two amplifiers per node, one for each direction.
[0006] FIG. 2 illustrates an alternative configuration according to
the related art for designing a bidirectional amplifier as
disclosed in U.S. Pat. No. 6,018,404 entitled "Bidirectional
Optical Telecommunication System Comprising a Bidirectional Optical
Amplifier." The bidirectional amplifier configuration includes four
wavelength (A) selective optical couplers 221-224, one
unidirectional optical amplifying unit 220, two optical connectors
206, 207 and portions 225, 226, 227, 228 of passive optical fiber.
The components are coupled with each other to form an optical
bridge connection. This configuration uses only one amplifier 220.
However, it does not achieve a useful gain when the typical 40 dB
optical return loss is taken into consideration.
[0007] As illustrated in FIG. 2, two signals .lamda..sub.1 and
.lamda..sub.2 pass along a fiber, in opposite direction. The fiber
is connected via connectors 206 and 207. Wavelength selective
couplers 221-223, split the signals so that they enter the optical
amplifier 220 from the same direction, are amplified, and then
split by the wavelength couplers 221, 223, and 224 to continue
their travel along a common fiber in opposite directions. In the
operation of the system described, some of the signals are leaked
in the wrong direction (e.g., leakage of amplified signal
.lamda..sub.1 254 through coupler 224 that is reflected back 252
from coupler 221 to connector 206), which is called optical return
loss (ORL). The general formula that governs the return loss
is:
P.sub.return=P.sub.in+G-2L.sub.isolation (1)
ORL=P.sub.in-P.sub.return, (2)
where, P is power, G is amplifier gain, L.sub.isolation is
isolation loss through the device and ORL is optical return loss.
Typically, L.sub.isolation for conventional filters, couplers and
the like is 20 dB. Accordingly the maximum gain G.sub.max
calculated for a four module system is:
G.sub.max=2L.sub.isolation-ORL=2L.sub.isolation-40=0 (3)
Applying this general equation to the configuration illustrated in
FIG. 2 yields:
P.sub.return=P.sub.in+G-L.sub.224-L.sub.221; and
G.sub.max=L.sub.224+L.sub.221-ORL=20+20-40=0 (4)
where L.sub.224 and L.sub.221 are the isolation losses through
those corresponding devices. As determined in the foregoing
sections, G.sub.max should be set to zero to avoid excessive
amplified signal leakage. Additionally, the four-port configuration
also suffers from poor performance when there is a fiber break,
which can result in a 14 dB back-reflection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Advantages of embodiments of the present invention will be
apparent from the following detailed description of the preferred
embodiments thereof, which description should be considered in
conjunction with the accompanying drawings in which:
[0009] FIG. 1 illustrates a bidirectional communication system in
accordance with the related art;
[0010] FIG. 2 illustrates an optical line amplifier node in
accordance with the related art;
[0011] FIG. 3 illustrates an optical line amplifier node in
accordance with at least one embodiment of the invention;
[0012] FIG. 4 is a graph of the maximum gain for various
configurations of at least one embodiment of a single-fiber
bidirectional optical amplifier compared to conventional
systems;
[0013] FIG. 5 illustrates a bidirectional communication system in
accordance with at least one embodiment of the invention; and
[0014] FIG. 6 illustrates a method of single amplifier
amplification of multiple signals, in accordance with at least one
exemplary embodiment of the invention.
DETAILED DESCRIPTION
[0015] Aspects of the invention are disclosed in the following
description and related drawings directed to specific embodiments
of the invention. Alternate embodiments may be devised without
departing from the spirit or the scope of the invention.
Additionally, well-known elements of exemplary embodiments of the
invention will not be described in detail or will be omitted so as
not to obscure the relevant details of the invention. Further, to
facilitate an understanding of the description discussion of
several terms used herein follows.
[0016] The expressions "communicates", "coupled", "connection", and
"connected" as used herein refers to any connection, coupling, link
and other methods/devices known by one skilled in the art by which
optical signals carried by one optical system element are imparted
to the "communicating" element. Further, the devices described can
be operatively connected (e.g., are not directly connected to one
another) and can be separated by intermediate optical components or
devices.
[0017] Additionally, the terns band-splitting filter and
band-splitting filter module (BSM) can be used interchangeably and
refer to any element that can separate and/or combine optical
signals propagating at separate frequencies. The signals may be
aggregated into frequency bands ("bands") that typically are
non-overlapping frequency ranges that can contain multiple signals,
as is known in the art.
[0018] Referring to FIG. 3, an optical amplifier module 300 in
accordance with at least one embodiment of the invention is
illustrated. The optical amplifier module 300 can be a
bidirectional optical amplifier, although the invention is not
limited to only bidirectional communication. For illustrative
purposes only, the optical amplifier module 300 will be assumed to
be a bidirectional optical amplifier 300, in accordance with at
least one exemplary embodiment. The bidirectional optical amplifier
300 can be used in a single-fiber as well as in fiber-pair
bidirectional links. For example, a single optical amplifier (OA)
is used to amplify optical dense wave division multiplexed (DWDM)
signals traveling in opposite directions, thus reducing equipment
cost. Channels propagating in opposite directions are chosen from
two non-overlapping bands (e.g., the C-Band, Red (R) band and Blue
(B) band). The bidirectional optical amplifier module 300 can
incorporate multiple band-splitting filter modules (e.g., six
band-splitting filter modules 311-316). Modules 311 through 314,
route the counter-propagating signals into the optical amplifier
320, then out into the signal's original propagating directions.
Modules 315 and 316 are used to provide increased optical return
loss of 40 dB in each direction to meet a 40 dB Optical Return Loss
(ORL) specification.
[0019] For example, the DWDM (or WDM) signals traveling in the
opposite directions are chosen to be from two non-overlapping bands
of the optical spectrum red (R) and blue (B). Band-splitting
modules 311-316 can be used to route the counter-propagating
signals to and from the OA 320. In accordance with at least one
embodiment of the invention, adding extra filtering (e.g., modules
315 and 316) improves the overall performance of the amplifier
module 300. Those skilled in the art will appreciate that modules
315 and 316 can be band specific filters or can be band-splitting
modules, which use only two of the three ports as illustrated.
Further, any element that passes the appropriate band and provides
additional isolation can be used for modules 315 and 316, such as
thin-film filters, fiber Bragg grating (FBG) filters, and array
waveguide (AWG) filters. However, those skilled in the art will
appreciate that the invention is not limited to the examples
provided.
[0020] Accordingly applying a similar gain calculation as provided
in Eq. 3 to the configuration of FIG. 3 yields:
G.sub.max=(L.sub.311+L.sub.313+L.sub.315).sub.--ORL (5)
where L.sub.311, L.sub.313, and L.sub.315 are the respective
isolation through each module for the blue signal. Note that only
one side of the return path (e.g., 313, 315, 311) after
amplification is used in the calculation of the maximum gain
G.sub.max as these will typically be balanced with the isolation
values in the other return path (313, 316, 314), for the red
signal. If these isolation values are not equal, then the G.sub.max
can be calculated using the return path that has the minimum
isolation values. For example, the isolation values can be
different if slightly different band-passing filters are used.
Likewise, manufacturing variations between any two modules might
differ by as much as couple dB.
[0021] However, in at least one embodiment, the values for the
filter modules 311-316 can be substantially the same nominal value
L. Therefore, equation 5 can be reduced to:
G.sub.max=3L-ORL_(6)
Using typical values for thin-film elements, L is equal to 20 dB
and as noted above the value for ORL is typically 40 dB. Applying
these values to equation 6 yields:
G.sub.max=3(20 dB).sub.--40 dB=20 dB. (7)
Accordingly, adding the additional filter modules (315, 316) allows
for a useful maximum gain of 20 dB.
[0022] However, those skilled in the art will appreciate that the
invention is not limited to any specific values. For example,
equations 5 or 6 can be used to easily determine the maximum gain
for any values or can be use to determined the required isolation
values for a desired maximum gain.
[0023] Accordingly, at least one embodiment of the invention can
include an optical amplifier module 300, as generally illustrated
in FIG. 3. A first band-splitting module (BSM) 311 can be coupled
to a first communication fiber 332 to receive a first signal (e.g.,
a Red band signal) propagating in a first direction (e.g., W-E). A
second BSM 314 can be coupled to a second communication fiber 334
to receive a second signal (e.g., a Blue band signal) propagating
in a second direction (e.g., E-W). A third BSM 312 can be coupled
to the first BSM 311 to receive the first signal, coupled to the
second BSM 314 to receive the second signal, and coupled to an
amplifier 320. The third BSM 312 is configured to combine the first
and the second signals and provide a combined signal traveling in a
common direction to the amplifier 320. For example, as discussed
above a BSM can split and/or combine signals having different
frequency bands. As illustrated, the third BSM 312 is a 3 port
device (R, B, and C) that can receive signals on the R and B ports
and output a combined signal (e.g., having both Red and Blue
signal) at the C port. Likewise, after the combined signal is
amplified, a fourth BSM 313 can be coupled to the amplifier 320 to
separate the combined signal into amplified first and amplified
second signals. A first filter 315 can be coupled between the first
BSM 311 and the fourth BSM 313 to receive the amplified second
signal from the fourth BSM 313 and to propagate the amplified
second signal to the first BSM 311. The first BSM 311 directs the
amplified second signal to the first communication fiber 332. A
second filter 316 can be configured to receive the amplified first
signal from the fourth BSM 313 and to propagate the amplified first
signal to the second BSM 314. Likewise, the second BSM 314 directs
the amplified first signal to the second communication fiber 334.
Accordingly, a common fiber can be used to propagate both signals
(e.g., Red and Blue bands) between nodes in an optical
communication network as further illustrated in FIG. 5.
[0024] FIG. 4 is a graph of the maximum gain for various
configurations of a single-fiber bidirectional optical amplifier
assuming an ORL value of 40 dB. As illustrated in FIG. 4, the
six-module system 420 according to embodiments of the invention
provides for a maximum gain of 20 dB using conventional thin-film
elements. As illustrated by line 410, conventional thin-film
elements typically have isolation values of 20 dB. The related art
four-module system as illustrated by line 430 does not allow for
any gain, if the system is going to meet the 40 dB ORL
specification. Likewise, a single module four-port thin-film device
as illustrated by line 440 does not allow for any gain, if the
system is going to meet the 40 dB ORL specification. For the
configurations illustrated by lines 430 and 440, devices with
significantly higher isolation values are required. However,
designing a system using the required high isolation devices is not
practical because of the lack of availability and increased costs
of these devices.
[0025] Referring to FIG. 5, a portion of a network 500 in
accordance with at least one embodiment of the invention is
illustrated. Network 500 has an east terminal 510 and west terminal
540. The east 510 and west 540 terminals communicate via lines
(e.g., 562, 564, 566) that interconnect the terminals and nodes
(e.g., optical line amplifier nodes 520 and 530). In contrast to
the system of FIG. 1, the present network can use one bidirectional
line. Further, as previously discussed, amplifiers (e.g., 300) can
be added to boost the signals, because of the distance between
terminals 510, 540. However, since the east and west signal traffic
(e.g., red or blue) can propagate on a single fiber, the red and
blue signals can be amplified as illustrated in FIG. 3 using a
common amplifier. Accordingly, since both east to west and west to
east signals are combined for amplification, the number of
amplifier modules can be reduced by half over the related art
system of FIG. 1 and still can meet the 40 dB ORL
specification.
[0026] In view of the foregoing disclosure, those skilled in the
art will recognize that embodiments of the invention include
methods of performing the sequence of actions, operations and/or
functions discussed herein. For example, FIG. 6 illustrates a
method in accordance with at least one exemplary embodiment. As
discussed above, multiple signals having multiple wavelengths can
propagate in opposite directions along a single optical fiber. The
method includes receiving a first signal propagating in a first
direction from a first port and second signal propagating in a
second direction from a second port, block 610. The first and
second signals are combined into a combined signal propagating in
one direction, block 620. The combined signal is then amplified,
block 630. The combined signal is then split into amplified first
and amplified second signals, block 640. The isolation loss of each
amplified signal is increase, block 650. Then, the amplified first
signal propagating in the first direction is output at the second
port and the amplified second signal propagating in the second
direction is output at the first port, block 660.
[0027] The foregoing discussion and related illustration is merely
an example of aspects of the invention and the invention is not
limited to this example. Further, other methods and alternatives
can be recognized by those skilled in the art, and the illustrated
example is not intended as limiting of the methods disclosed
herein.
[0028] Accordingly, the foregoing description and accompanying
drawings illustrate the principles, preferred embodiments and modes
of operation of the invention. However, the invention should not be
construed as being limited to the particular embodiments discussed
above.
[0029] Therefore, the above-described embodiments should be
regarded as illustrative rather than restrictive. Accordingly, it
should be appreciated that variations to those embodiments can be
made by those skilled in the art without departing from the scope
of the invention as defined by the following claims.
* * * * *